[quote author=“mckenzievmd”]Remember, selection pressure can produce modifications in invisible characteristics; MHC haplotypes in our immune systems, resistence of susceptibility to toxins, infectious agents, dietary tolerances.
Right, good point. But when you get large enough, diverse enough populations and travel and interbreeding is continuous, I think we can agree that the likelihood of any sort of large scale genetic change in a significant portion of the population is minimized.
[quote author=“mckenzievmd”]But I think there is insuficient evidence to declare us at a standstill.
Perhaps. I’d say it’s statistically very likely, though, with some fuzziness at the edges.
[quote author=“dougsmith”][quote author=“jimmiekeyes”]
I agree that we can force modification of the species and it will in all likelihood happen but that is not evolution.
Well, it would be evolution by artificial selection rather than by natural selection.
FWIW, I agree that the human race is basically at evolutionary stasis at this point, at least as regards natural selection. The fossil record gives ample reason to believe that once species become widely established they can remain unchanged for millions—even hundreds of millions—of years.
Evolution is evolution whether you force it ( ie: man made selective pressures) or whether its natural. But I was not referring to forcing anything. There are selective pressures in our environment all the time, and if those pressure remain in effect over the course of many generations those pressures will result in the evolution of the species. Humans are no different in that respect than any other living organism.
There are literally thousands of selective pressures that human beings are subjected to, from infectious diseases to pollution, emotional and financial pressures, environmental toxins and carcinogens etc etc. If any of these things affects one group more than another the group less affected will have a survival advantage and evolution contiues.
Hmm. Well, I’d certainly agree that we no longer have many trukly reproductively isolated groups, so changes divergent changes, and changes due to founder effects and genetic drift are unlikley (which is why I argued in previous threads against the genetic meaningfullness of human races). But I still think the population as a whole could change in significant ways under intense, probably artifical selection pressures, compared to where we are currently.
How about some totally made-up examples? Say that overpopulation becomes extreme enough that draconian and actually enforceable limits on reproduction develop. And say there are specific criteria for permission to reproduce based, as I imagine they would be, on some supposedly rational basis but largely based on the prejudices of the politically dominent culture. Maybe a given IQ score, or a certain facility with the technologies of the time require strong ability to divide attention among multiple information sources and tasks. Whatever. Couldn’t this create a situation in which diferential reproduction based on artificial selection would lead to significant changes in the genome?
Or a less artificial example. Suppose greater population densities and stresses leads to a barrage of infectious diseases and our medical technology doesn’t create a timely, effective solution. Variation in stress hormone responses and immune function that conferred differential resistence and thus differential reproduction might lead to changes in the genome. It is likely this has already happened, to some extent, due to the development of cities in human history, and the need for an immune system that can manage much higher and more persistent exposure to infectious agents.
Of course you’re talking about the world as it is now, and I can’t say for sure that we are under selection pressures that are altering the genome in meaningful ways. We may not be. But, as I always seem to be doing, I caution againstthe reasonableness of the idea and the difficulty in identifying such forces as being taken as evidence that they do not exist. On what do you base you probabilistic assessment?
Here’s a link on the subject of lactose tolerance:
And here’s one ont he possibility of ongoing evolution in genes involved in brain development:
There are lots of other similar studies. They all, of course, refer to changes in pre-modern times, most > 5000 years ago. But while it is a reasonable hypothesis that modern technology (especially medicine and transportation) have reduced selection pressures significantly, I still think it’s going too far to say that they have eliminated any chance of significant genetic changes.
The most detailed analysis to date of how humans differ from one another at the DNA level shows strong evidence that natural selection has shaped the recent evolution of our species, according to researchers from Cornell University, Celera Genomics and Celera Diagnostics.
[quote author=“mckenzievmd”] But I still think the population as a whole could change in significant ways under intense, probably artifical selection pressures, compared to where we are currently.
Right; I was referring to natural selection pressures.
[quote author=“mckenzievmd”]On what do you base you probabilistic assessment?
Well, on the fact that we are a large, genetically diverse, mobile, interbreeding population. Leaving aside artificial selection, I’d say we’re most likely at stasis, and stasis can last a very long time indeed.
But of course, the possibility of artificial manipulation does change the game.
Even IF humans have stopped or slowed down in their evolutionary process, what concerns me is, the evolution of apes- the hairy kind, not us hairless apes. It won’t happen in our lifetimes, but one day we may find that we are living the science fiction “Planet of the Apes”. If we humans keep treating our “cousins” as we do, we may find that one day they are capable of retolerating and start attacking us for how we have treated them, even if they do know there are good humans out here like Diane Fossey and Jane Goodall. Eventually, the few won’t matter and they won’t care if the human is a good human or a bad human.
It is one science fiction, out of so many that don’t, that could become a reality a few hundred years from now. Unfortunately, I won’t be alive to say, “See? I told you one day this could happen, but you blew me off and laughed at me, just as you did Darwin when he was alive.” Of course, neither will the people who laughed and blew me off as some dreamy/fantasizing and wishful person who anthropomorphisizes animals.
At one time, cats were considered gods and they never have forgotten that, might one day be said, “At one time, apes were considered just dumb animals for poaching, experimenting on, and driven to near extinction, which they have never forgotten and now we humans are paying the price.” While cats as gods is a myth, apes declaring war on humans could one day be a fact.
I wasn’t saying there was. What I’m trying to say is, Chimps are figuring out how to make weapons much like our prehistoric ancestors did. Those who observe chimps have seen how they make spears to hunt other animals. One day their ancestors will figure out something more advance than spears and get the bright idea to use them on Humans who invade their land. I don’t think it takes rocket science to figure out what the future generations of chimp’s potential might be, esp if one were to factor in evolution.
I am not saying that they will look like the chimps on “Planet of the Apes” necessarily, but the potential that their brains grow, like ours did over a course of time, therefore their intelligence will grow and the potential for them to constantly walk on twos instead of fours occassionally is there too. Just as we went from Lucy to this and that to homoerectus to homosapien, if you stick with evolution, chimps could be the ancestors of something else that manages to carry the stories of what humans do with them.
Sadly, I think it’s a lot more likely there won’t be any “hairy apes” left in the not-too-distant future. We’re pressing small isolated populations pretty hard already, and we show no signs of getting our reproduction under control, so I suspect that pressure will only get worse. But, there’s always hope.
To repeat what has already been said.
1) Evolutionary changes take place over thousands of years unless there is a catastrophic environmental event. For example, had HIV shown up two hundred years ago, the human population today would be made up almost entirely of descendants of those one in one hundred and forty people who have a gene that blocks HIV entrance into the host’s cells. So, I think, yes, there are evolutionary pressures still occurring and those people, no matter how much intermixing of groups, who have the genes that deal with the changes most effectively will very gradually breed preferentially.
2) While those with more education and/or higher financial status (assuming these are correlated with intelligence) tend to have smaller families thus shifting the genetic pool toward the lower intelligence people. However, I would guess that in the near future many will opt to have a bit of genetic engineering done on their children to enhance their intelligence. Of course, there will also be those who want their children to be more attractive, have more athletic ability, have bigger body parts, etc.
3) Although we seem to be able to control our environment at present, if global warming continues as predicted, we may have far more environmental pressures than we expect. As genetically engineered bacteria and viruses become easier to produce, it’s likely that fanatics will do so and cause pandemics, another unexpected environmental pressure.
4) Species occur, flourish, and go extinct over a few hundred, to a few hundred million years. We’ve got a few billion years before the sun envelops the earth. During that time, the earth should go through a wide variety of new species replacing the present ones. Looking back to the paleozoic bizarre variety of life, I don’t think we have to worry about running out of new kinds before the universe ceases to be warm enough to support chemical reactions.
The term “meme” (IPA: /miːm/, rhyming with “theme”; commonly pronounced in the US as /mɛm/, rhyming with “gem”), coined/popularized in 1976 by the biologist Richard Dawkins, refers to a “unit of cultural information” which can propagate from one mind to another in a manner analogous to genes (i.e., the units of genetic information).
Dawkins gave as examples of memes: tunes, catch-phrases, beliefs, clothes fashions, ways of making pots, or of building arches. A meme, he said, propagates itself as a unit of cultural evolution and diffusion—analogous in many ways to the behavior of the gene. Often memes propagate as more-or-less integrated cooperative sets or groups, referred to as memeplexes or meme-complexes.